Microbial Metabolism Questions and Answers

Answer: D

Correct answer: is heat and pH labile

Enzymes are proteins, and their activity depends on a precise three-dimensional shape, so they are denatured by heat and by pH extremes. The other statements are all false: an enzyme is highly specific for its substrate, and it is neither consumed by the reaction nor built into the products - which is why a small amount can turn over a great deal of substrate.

Answer: D

Correct answer: active site

The apoenzyme is the protein part of a conjugated enzyme, and it carries the active site - the pocket whose shape and chemistry determine which substrate is bound. The non-protein cofactor or coenzyme completes it; apoenzyme plus cofactor is the active holoenzyme.

Answer: B

Correct answer: vitamins

Many coenzymes are derived from vitamins, which is precisely why vitamins are needed in the diet in such small amounts: NAD from niacin, FAD from riboflavin, coenzyme A from pantothenate, TPP from thiamine. Metal ions are cofactors but not coenzymes, which are organic.

Answer: B

Correct answer: exoenzyme

Cellulose is a huge insoluble polymer that cannot cross the cell membrane, so the fungus secretes an exoenzyme to break it down outside the cell and then absorbs the sugars released. Endoenzymes work within the cell.

Answer: B

Correct answer: chemical

Living systems run on chemical energy - energy held in bonds, and moved about in compounds such as ATP. Radiant energy matters only where photosynthesis captures it, and it is converted to chemical form at once.

Answer: B

Correct answer: ATP

ATP is the cell’s energy currency. Catabolism captures released energy by phosphorylating ADP, and anabolism spends it by hydrolysing ATP back to ADP and phosphate at the point where work must be done. Coupling the two through a common intermediate is what lets one pathway pay for another.

Answer: A

Correct answer: release potential energy

An exergonic reaction has a negative \(\Delta G\): the products hold less free energy than the reactants, so energy is released and the reaction proceeds spontaneously. Endergonic reactions consume energy and must be coupled to an exergonic one to go at all.

Answer: C

Correct answer: NADH

NADH is the reduced form - NAD⁺ that has accepted two electrons and a proton. NAD and FAD as written are the oxidised forms, and ADP is a nucleotide of energy transfer, not of redox.

Answer: C

Correct answer: The cytoplasm

Bacteria have no mitochondria, so the Krebs cycle enzymes are dissolved in the cytoplasm. The electron transport chain, by contrast, is embedded in the plasma membrane, which is the prokaryotic counterpart of the inner mitochondrial membrane.

Answer: C

Correct answer: direct transfer of a phosphate group from a phosphorylated compound to ADP

Here an enzyme moves a phosphate straight from a high-energy intermediate onto ADP, as happens twice in glycolysis. It requires no membrane and no electron transport chain, which is why fermenting organisms depend on it entirely.